1. Field of the Invention
The invention relates to cathode structures and somewhat more particularly to polarographic cathode structures useful in physiological mediums.
2. Prior Art
S. Sinmaru et al. in an article entitled "Catheter-Mounted Oxygen Electrode For Monitoring Oxygen Tension", appearing in "Cardiovascular Research Center Bulletin", April-June 1972, page 112, describe a cathode for polarographic measurements comprised of a steel wire having a piece of a gold wire attached to the proximal tip of the steel wire. The steel wire with the attached gold wire is coated or sealed within an insulating material and this insulating envelope is further sheated in a layer of a body-tolerable material. The proximal tip of the gold wire is covered with an oxygen-permeable membrane and contacts the physiological medium. The manufacture of this type of polarographic cathode structure is complicated. Each steel wire piece must be individually connected to a gold wire piece, for example, by spot welding. Accordingly, such cathodes are comparatively expensive.
Another known polarographic cathode structure is comprised of a cable section having at least one continuous strand of a precious-metal wire therein, preferably a gold wire, which is enveloped in an insulating material. In the manufacture of this type of cathode structure, cut sections or pieces of an insulated precious metal cable are utilized. Cathode structures of this type have proven successful for polarographic measurement in physiological medium. The manufacture of this type of cathode structure is relatively simple. However, because of the need for continuous gold wires, these cathodes are relatively expensive. Economical considerations play a major role in the use of such cathodes which, for medical reasons, are preferably developed as throw-away articles or as articles of one-time use. Further, gold wires having small diameters are mechanically weak so that special care is required during the manufacture and handling of cathodes containing such gold wires.